This invention relates to cell biology, physiology and medicine, and concerns an 88 kDa glycoprotein growth factor (xe2x80x9cGP88 xe2x80x9d) and compositions and methods which affect the expression and biological activity of GP88. These compositions and methods are useful for diagnosis and treatment of diseases including cancer.
Several publications are referenced herein by Arabic numerals within parenthesis. Full citations for these references may be found at the end of the specification immediately preceding the claims.
The proliferation and differentiation of cells in multicellular organisms is subject to a highly regulated process (1). A distinguishing feature of cancer cells is the absence of control over this process; proliferation and differentiation become deregulated resulting in uncontrolled growth. Significant research efforts have been directed toward better understanding this difference between normal and tumor cells. One area of research focus is growth factors and, more specifically, autocrine growth stimulation.
Growth factors are polypeptides which carry messages to cells concerning growth, differentiation, migration and gene expression (2). Typically, growth factors are produced in one cell and act on another cell to stimulate proliferation. However, certain malignant cells, in culture, demonstrate a greater or absolute reliance on an autocrine growth mechanism (3). Malignant cells which observe this autocrine behavior circumvent the regulation of growth factor production by other cells and are therefore unregulated in their growth.
Study of autocrine growth control advances understanding of cell growth mechanisms and leads to important advances in the diagnosis and treatment of cancer. Toward this end, a number of growth factors have been studied, including insulin-like growth factors (xe2x80x9cIGF1 xe2x80x9d and xe2x80x9cIGF2 xe2x80x9d), gastrin-releasing peptide (xe2x80x9cGRPxe2x80x9d), transforming growth factors alpha and beta (xe2x80x9cTGF-axe2x80x9d and xe2x80x9cTGF-bxe2x80x9d), and epidermal growth factor (xe2x80x9cEGFxe2x80x9d).
The present invention is directed to a recently discovered growth factor. This growth factor was first discovered in the culture medium of highly tumorigenic xe2x80x9cPC cells,xe2x80x9d an insulin-independent variant isolated from the teratoma derived adipogenic cell line 1246. This growth factor is referred to herein as xe2x80x9cGP88.xe2x80x9d GP88 has been purified and structurally characterized (4). Amino acid sequencing of GP88 indicates that GP88 has amino acid sequence similarities with the mouse granulin/epithelin precursor.
Granulins/epithelins (xe2x80x9cgrn/epixe2x80x9d) are 6 kDa polypeptides and belong to a novel family of double cysteine rich polypeptides (5, 6). U.S. Pat. No. 5,416,192 (Shoyab et al.) is directed to 6 kDa epithelins, particularly epithelin 1 and epithelin 2. According to Shoyab, both epithelins are encoded by a common 63.5 kDa precursor, which is processed into smaller forms as soon as it is synthesized, so that the only natural products found in biological samples are the 6 kDa forms. Shoyab et al. teaches that the epithelin precursor is biologically inactive.
Contrary to the teachings of Shoyab et al., the inventor""s laboratory has demonstrated that the precursor is not always processed as soon as it is synthesized. Studies, conducted in part by this inventor, have demonstrated that the precursor (i.e., GP88) is in fact secreted as an 88 kDa glycoprotein with an N-linked carbohydrate moiety of 2 kDa (4). Analysis of the N-terminal sequence of GP88 indicates that GP88 starts at amino acid 17 of the grn/epi precursor, demonstrating that the first 17 amino acids from the protein sequence deduced from the precursor cDNA correspond to a signal peptide compatible with targeting for membrane localization or for secretion (4).
Also in contrast to the teachings of Shoyab et al., GP88 is biologically active and has growth promoting activity, particularly as an autocrine growth factor for the producer cells.
The inventor has now unexpectedly discovered that a glycoprotein (GP88), which is expressed in a tightly regulated fashion in normal cells, is overexpressed and unregulated in highly tumorigenic cells derived from the normal cells, that GP88 acts as a stringently required growth stimulator for the tumorigenic cells and that inhibition of GP88 expression or action in the tumorigenic cells results in an inhibition of the tumorigenic properties of the overproducing cells.
It is an object of this invention to provide GP88 antagonizing compositions capable of inhibiting the expression or activity of GP88.
A further object of the invention is to provide methods for treating diseases associated with a defect in GP88 quantity or activity such as but not limited to cancer in mice or humans.
Another object of the invention is to provide methods for determining the susceptibility of a subject to diseases associated with a defect in GP88 expression or action.
Yet another object of the invention is to provide methods for measuring susceptibility to GP88 antagonizing therapy.
Yet another object of the invention is to provide methods, reagents, and kits for the in vitro and in vivo detection of GP88 and tumorigenic activity in cells.
Additional objects and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by the practice of the invention.
To achieve the objects and in accordance with the purpose of the invention, as embodied and properly described herein, the present invention provides compositions for diagnosis and treatment of diseases such as but not limited to cancer in which cells exhibit an altered expression of GP88 or altered response to GP88.
Use of the term xe2x80x9caltered expressionxe2x80x9d herein means increased expression or overexpression of GP88 by a factor of at least two-fold, and at times by a factor of 10 or more, based on the level of mRNA or protein as compared to corresponding normal cells or surrounding peripheral cells. The term xe2x80x9caltered expressionxe2x80x9d also means expression which became unregulated or constitutive without being necessarily elevated. Use of the terms increased or altered xe2x80x9cresponsexe2x80x9d to GP88 means a condition wherein increase in any of the biological functions (e.g., growth, differentiation, viral infectivity) conferred by GP88 results in the same or equivalent condition as altered expression of GP88.
Use of the term xe2x80x9cGP88xe2x80x9d herein means epithelin/granulin precursor in cell extracts and extracellular fluids, and is intended to include not only GP88 according to the amino acid sequences included in FIG. 8 or 9, which are of mouse and human origins, but also GP88 of other species. In addition, the term also includes functional derivatives thereof having additional components such as a carbohydrate moiety including a glycoprotein or other modified structures.
Also intended by the term GP88 is any polypeptide fragment having at least 10 amino-acids present in the above mentioned sequences. Sequences of this length are useful as antigens and for making immunogenic conjugates with carriers for the production of antibodies specific for various epitopes of the entire protein. Such polypeptides are useful in screening such antibodies and in the methods directed to detection of GP88 in biological fluids. It is well known in the art that peptides are useful in generation of antibodies to larger proteins (7). In one embodiment of this invention, it is shown that peptides from 12-19 amino-acids in length have been successfully used to develop antibodies that recognize the full length GP88.
The polypeptide of this invention may exist covalently or non-covalently bound to another molecule. For example, it may be fused to one or more other polypeptides via one or more peptide bonds such as glutathione transferase, poly-histidine, or myc tag.
The polypeptide is sufficiently large to comprise an antigenetically distinct determinant or epitope which can be used as an immunogen to reproduce or test antibodies against GP88 or a functional derivative thereof.
One embodiment includes the polypeptide substantially free of other mammalian peptides. GP88 of the present invention can be biochemically or immunochemically purified from cells, tissues or a biological fluid. Alternatively, the polypeptide can be produced by recombinant means in a prokaryotic or eukaryotic expression system and host cells.
xe2x80x9cSubstantially free of other mammalian polypeptidesxe2x80x9d reflects the fact that the polypeptide can be synthesized in a prokaryotic or a non-mammalian or mammalian eukaryotic organism, if desired. Alternatively, methods are well known for the synthesis of polypeptides of desired sequences by chemical synthesis on solid phase supports and their subsequent separation from the support. Alternatively, the protein can be purified from tissues or fluids of mammals where it naturally occurs so that it is at least 90% pure (on a weight basis) or even 99% pure, if desired, of other mammalian polypeptides, and is therefore substantially free from them. This can be achieved by subjecting the tissue extracts or fluids to standard protein purification such as on immunoabsorbants bearing antibodies reactive against the protein. One embodiment of the present invention describes purification methods for the purification of naturally occurring GP88 and of recombinant GP88 expressed in baculovirus infected insect cells. Alternatively, purification from such tissues or fluids can be achieved by a combination of standard methods such as but not limited to the ones described in reference (4).
As an alternative to a native purified or recombinant glycoprotein or polypeptide, xe2x80x9cGP88 xe2x80x9d is intended to also include functional derivatives. By functional derivative is meant a xe2x80x9cfragment,xe2x80x9d xe2x80x9cvariant,xe2x80x9d xe2x80x9canalog, xe2x80x9d or xe2x80x9cchemical derivativexe2x80x9d of the protein or glycoprotein as defined below. A functional derivative retains at least a portion of the function of the full length GP88 which permits its utility in accordance with the present invention.
A xe2x80x9cfragmentxe2x80x9d of GP88 refers to any subset of the molecule that is a shorter peptide. This corresponds for example but is not limited to regions such as K19T and S14R for mouse GP88, and E19V and A14R (equivalent to murine K19T and S14R, respectively) for human GP88.
A xe2x80x9cvariantxe2x80x9d of GP88 refers to a molecule substantially similar to either the entire peptide or a fragment thereof. Variant peptides may be prepared by direct chemical synthesis of the variant peptide using methods known in the art.
Alternatively, amino acid sequence variants of the peptide can be prepared by modifying the DNA which encodes the synthesized protein or peptide. Such variants include, for example, deletions, insertions, or substitutions of residues within the amino-acid sequence of GP88. Any combination of deletion, insertion, and substitution may also be made to arrive at the final construct, provided the final construct possesses the desired activity. The mutation that will be made in the DNA encoding the variant peptide must not alter the reading frame and preferably will not create complementary regions that could produce secondary mRNA structures. At the genetic level these variants are prepared by site directed mutagenesis (8) of nucleotides in the DNA encoding the peptide molecule thereby producing DNA encoding the variant, and thereafter expressing the DNA in recombinant cell culture. The variant typically exhibits the same qualitative biological activity as the nonvariant peptide.
An xe2x80x9canalogxe2x80x9d of GP88 protein refers to a non-natural molecule substantially similar to either the entire molecule or a fragment thereof.
A xe2x80x9cchemical derivativexe2x80x9d contains additional chemical moieties not normally a part of the peptide or protein. Covalent modifications of the peptide are also included within the scope of this invention. Such modifications may be introduced into the molecule by reacting targeted amino-acid residues of the peptide with an organic derivatizing agent that is capable of reacting with selected side chains or terminal amino-acid residues. Most commonly derivatized residues are cysteinyl, histidyl, lysinyl, arginyl, tyrosyl, glutaminyl, asparaginyl and amino terminal residues. Hydroxylation of proline and lysine, phosphorylation of hydroxyl groups of seryl and threonyl residues, methylation of the alpha-amino groups of lysine, histidine, and histidine side chains, acetylation of the N-terminal amine and amidation of the C-terminal carboxylic groups. Such derivatized moieties may improve the solubility, absorption, biological half life and the like. The moieties may also eliminate or attenuate any undesirable side effect of the protein and the like. In addition, derivatization with bifunctional agents is useful for cross-linking the peptide to water insoluble support matrices or to other macromolecular carriers. Commonly used cross-linking agents include glutaraldehyde, N-hydroxysuccinimide esters, homobifunctional imidoesters, 1,1-bis(-diazoloacetyl)-2-phenylethane, and bifunctional maleimides. Derivatizing agents such as methyl-3-[9p-azidophenyl)]dithiopropioimidate yield photoactivatable intermediates that are capable of forming crosslinks in the presence of light. Alternatively, reactive water-insoluble matrices such as cyanogen bromide activated carbohydrates and the reactive substrates described in U.S. Pat. Nos. 3,969,287 and 3,691,016 may be employed for protein immobilization.
Use of the term GP88 xe2x80x9cantagonizing agentsxe2x80x9d herein means any composition that inhibits or blocks GP88 expression, production or secretion, or any composition that inhibits or blocks the biological activity of GP88. This can be achieved by any mode of action such as but not limited to the following:
(A) GP88 antagonizing agents include any reagent or molecule inhibiting GP88 expression or production including but not limited to:
(1) antisense GP88 DNA or RNA molecules that inhibit GP88 expression by inhibiting GP88 translation;
(2) reagents (hormones, growth factors, small molecules) that inhibit GP88 mRNA and/or protein expression at the transcriptional, translational or post-transaltional levels;
(3) factors, reagents or hormones that inhibit GP88 secretion;
(B) GP88 antagonizing agents also include any reagent or molecule that will inhibit GP88 action or biological activity such as but not limited to:
(1) neutralizing antibodies to GP88 that bind the protein and prevent it from exerting its biological activity;
(2) antibodies to the GP88 receptor that prevent GP88 from binding to its receptor and from exerting its biological activity;
(3) competitive inhibitors of GP88 binding to its receptors;
(4) inhibitors of GP88 signaling pathways.
Specific examples presented herein provide a description of preferred embodiments, particularly the use of neutralizing antibodies to inhibit GP88 biological action and the growth of the highly tumorigenic PC cells; the use of antisense GP88 cDNA and antisense GP88 oligonucleotides to inhibit GP88 expression leading to inhibition of the tumorigenic properties of the PC cells; characterization of GP88 receptors on cell surfaces of several cell lines including the mammary epithelial cell line C57MG, the 1246 and PC cell lines and the mink lung epithelial cell line CCL64.
In one embodiment of the invention, the GP88 antagonizing agents are antisense oligonucleotides to GP88. The antisense oligonucleotides preferably inhibit GP88 expression by inhibiting translation of the GP88 protein.
Alternatively, such a composition may comprise reagents, factors or hormones that inhibit GP88 expression by regulating GP88 gene transcriptional activity. Such a composition may comprise reagents, factors or hormones that inhibit GP88 post-translational modification and its secretion. Such a composition may comprise reagents that act as GP88 antagonists that block GP88 activity by competing with GP88 for binding to GP88 cell surface receptors. Alternatively, such a composition may comprise factors or reagents that inhibit the signaling pathway transduced by GP88 once binding to its receptors on diseased cells.
Alternatively, the composition may comprise reagents that block GP88 action such as an antibody specific to GP88 that neutralizes its biological activity, or an antibody to the GP88 receptor that blocks its activity.
The antibodies of the invention (neutralizing and others) are preferably used as a treatment for cancer or other diseases in cells which exhibit an increased expression of GP88. By the term xe2x80x9cneutralizingxe2x80x9d it shall be understood that the antibody has the ability to inhibit or block the normal biological activity of GP88, including GP88""s ability to stimulate cell proliferation or to induce tumor growth in experimental animals and in humans. An effective amount of anti-GP88 antibody is administered to an animal, including humans, by various routes. In an alternative embodiment, the anti-GP88 antibody is used as a diagnostic to detect cells which exhibit an altered (increased) expression of GP88 as occurring in diseases such as but not limited to cancers, and to identify diseased cells whose growth is dependent on GP88 and which will respond to GP88 antagonizing therapy. In yet another embodiment, the anti-GP88 antibody is used to deliver compounds such as cytotoxic factors or antisense oligonucleotides to cells expressing or responsive to GP88.
The antisense oligonucleotides of the invention are also used as a treatment for cancer in cells which exhibit an increased expression of GP88. An effective amount of the antisense oligonucleotide is administered to an animal, including humans, by various routes.
The present invention also provides a method for determining the susceptibility to diseases associated with a defect in GP88 expression or action which comprises obtaining a sample of biological fluid or tissue and measuring the amount of GP88 in the fluid or tissue or measuring the susceptibility of the cells to respond to GP88. In the case of cancer, the amount of GP88 being proportional to the susceptibility to the cancer.
The present invention also provides a method for measuring the degree of severity of cancer which comprises obtaining a sample of biological fluid or tissue and measuring the amount of GP88 in the fluid or tissue sample, the amount of GP88 being proportional to the degree or severity of the cancer.
The present invention also provides a method for measuring susceptibility to GP88 antagonizing therapy which comprises obtaining a sample of the diseased tissue (biopsy), maintaining the cells derived from the sample in culture, treating the cells derived from the culture with anti-GP88 neutralizing antibody and determining if the neutralizing antibody inhibits the cell growth. Ability of the antibody to inhibit cell growth is indicative that the cells are dependent on GP88 to proliferate and is predictive that GP88 antagonizing therapy will be efficacious.
The present invention also provides a method for determining the susceptibility to cancer associated with an abnormality in GP88 receptor level or activity which comprises obtaining a sample of tissue and measuring the amount of GP88 receptor protein or mRNA in the tissue or measuring the tyrosine kinase activity of the receptor in the tissue (GP88 binding to its receptor induces tyrosine phosphorylation of cellular proteins including the receptor for G88).
The present invention also provides a method for targeting GP88 antagonizing reagents to the diseased site by conjugating them to an anti-GP88 antibody or an anti-GP88 receptor antibody.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.